Adhesive, process for the preparation thereof, and process for mounting components

ABSTRACT

The invention presents an adhesive not impairing components poor in heat resistance in heating and curing, excellent in storage stability, and free from sagging due to heating.  
     Comprising 100 parts by weight of an epoxy resin having a content of mononuclear components of 87 to 100% by weight, 20 to 80 parts by weight of a latent curing agent, 2 to 40 parts by weight of an inorganic filler, 1 to 15 parts by weight of a thixotropic agent, and 0.1 to 5 parts by weight of a pigment, the epoxy resin and latent curing agent are preliminarily dispersed, heated, dissolved and cooled, and then the inorganic filler, thixotropic agent and pigment are dispersed to prepare.

TECHNICAL FIELD

[0001] The present invention relates to an adhesive preferably used inmounting of components such as electronic parts, a process forpreparation thereof, and a process for mounting components by using thisadhesive.

BACKGROUND ART

[0002] As an adhesive suited to mounting of electronic components, anadhesive composed of epoxy resin of standard purity, amine hardener,thixotropic agent, inorganic filler, and pigment is disclosed inJapanese Laid-open Patent No. 1-2493.

[0003] Hitherto, when mounting electronic components on a circuit board,a mounting method comprises the steps of applying a mounting adhesive onspecified positions on a circuit board, putting electronic components onthe applied adhesive positions, heating and curing the adhesive,applying flux on the circuit board, and immersing the circuit board inmolten solder to solder and bond the electronic components and thecircuit board.

[0004] However, the conventional adhesive for mounting electroniccomponents was high in curing temperature and may damage the componentspoor in heat resistance when curing, and as a countermeasure,conventionally, a large content of amine hardener was mixed in theadhesive for mounting electronic components.

[0005] In the existing adhesive for mounting electronic components,nevertheless, if a large content of amine hardener is mixed in, it mustbe kept within a range for assuring storage stability, and in such acase, yet, the curing temperature is still high, and the components poorin heat resistance may be damaged when curing. Still worse, if a largecontent of amine hardener is thus blended, the adhesive may sag andspread when heating and curing, and may be adhered to the electrode onthe circuit board by this sagging phenomenon due to heating, and whenthe adhesive is adhered to the electrode, it is hard to solder theelectronic component on the electrode.

DISCLOSURE OF THE INVENTION

[0006] In the light of the problems of the prior art, therefore, it isan object of the invention to present an adhesive which can be cured atlow temperature, does not impair components poor in heat resistance orspoil storage stability, and is free from sagging due to heating, aprocess for the preparation thereof, and a process for mountingcomponents.

[0007] The adhesive of the invention comprises 100 parts by weight of anepoxy resin having a content of mononuclear components of 87 to 100% byweight, and 20 to 80 parts by weight of a latent curing agent. By usingthe epoxy resin having a high content of mononuclear components, andusing the latent curing agent as the hardener, the heating temperaturein heating and curing can be lowered by the high content of thehardener, so that the adhesive lowered in the damage rate of componentsand excellent in storage stability can be obtained.

[0008] It further comprises 2 to 40 parts by weight of an inorganicfiller, 1 to 15 parts by weight of a thixotropic agent, and 0.1 to 5parts by weight of a pigment, and therefore the adhesive strength isenhanced and stringing is prevented, so that the adhesive havingproperties required as the adhesive for mounting components may beobtained.

[0009] This adhesive is prepared by preliminarily dispersing, heating,dissolving and cooling the epoxy resin and latent curing agent, and thendispersing the inorganic filler, thixotropic agent and pigment. Bydefining the heating temperature in heating and dissolving at 30 to 50°C. and heating time at 1 to 50 hours, phenomenon of sagging due toheating in heating and curing the adhesive can be prevented.

[0010] In the method of mounting components according to the invention,the adhesive comprising 100 parts by weight of the epoxy resin, 20 to 80parts by weight of the latent curing agent, 2 to 40 parts by weight ofthe inorganic filler, 1 to 15 parts by weight of the thixotropic agent,and 0.1 to 5 parts by weight of the pigment is prepared, and this methodcomprises the steps of applying the adhesive on specified positions onthe board, putting components on the applied adhesive positions, andheating and curing the adhesive, and it is intended to mount thecomponents without raising the heating and curing temperature. Moreover,when the heating and curing peak temperature in heating and curing iscontrolled at 100° C. or less and the heating time within 30 to 300seconds, damage of components poor in heat resistance can be prevented.

[0011] Besides, after heating and curing the adhesive, by applying fluxon the board, the board is immersed in a molten solder, so that thecomponents and board can be soldered and bonded.

BEST MODE OF CARRYING OUT THE INVENTION

[0012] According to an embodiment of the invention, an adhesive formounting components, a process for the preparation thereof, and aprocess for mounting electronic components by using the same aredescribed below.

[0013] The components of the adhesive used herein are as follows. Epoxyresin A: Epicoat 806L (Yuka Shell Epoxy Co.) (content of mononuclearcomponents 87 to 100% by weight) Epoxy resin B: Epicoat 828 (Yuka ShellEpoxy Co.) (content of mononuclear components 87% by weight or less)Hardener A: Fujicure FXE1000 (Fuji Kasei Co.) (aminoureade latent curingagent) Hardener B: Amicure PN23 (Ajinomoto) (amine curing agent)Inorganic filler: Mistron CB (Nippon Mistron) Thixotropic agent: AerosilRY200 (Nippon Aerosil) Pigment: Carmine 6B (Dainippon Ink)

[0014] A roll dispersion type agitating machine was used in mixing.

[0015] Measuring methods and evaluating methods of characteristics wereas follows.

[0016] Component damage rate: The adhesive is applied on the circuitboard by an adhesive applicator, cylindrical aluminum electrolyticcapacitors are mounted by a component mounting machine, the adhesive isheated and cured in a furnace in a profile for curing completely eachadhesive, the number of damages (a) in 100 positions of components iscounted, and the component damage rate (%) is calculated in the formula(a/100)×100%.

[0017] Heating sag rate: The adhesive is applied in a circle on thecircuit board, the applied diameter r0 [mm] is measured, and it isheated and cured in a furnace, and the applied diameter r1 [mm] ismeasured, and the heating sag rate (%) is calculated in the formula{(r1−r0)/r0}×100%.

[0018] Damage rate of components poor in heat resistance: The adhesiveis applied on the circuit board by an adhesive applicator, LEDcomponents are mounted by a component mounting machine, the adhesive isheated and cured in a furnace in a profile for curing completely eachadhesive, the number of damages (b) in 100 positions of components iscounted, and the damage rate of components poor in heat resistance (%)is calculated in the formula (b/100)×100%.

[0019] Storage stability: The viscosity η0 right after manufacture ofthe adhesive is measured by type E viscometer, and after leaving theadhesive for 30 days at 25+/−1° C., the viscosity η1 is measured again,and it is judged if the storage stability approval condition of(η1/η0)<2 is satisfied or not.

[0020] First, using 100 parts by weight of epoxy resin A as the adhesivemain ingredient, the number of parts by weight of each component thatcan be blended was studied. The following results were obtained.

[0021] As for Mistron CB (Nippon Mistron) as the inorganic filler, theupper limit of an adequate content capable of maintaining properties asadhesive is 40 parts by weight. The minimum content showing effects ofaddition of inorganic filler is 2 parts by weight.

[0022] As for Aerosil YR200 (Nippon Aerosil) as thixotropic agent, theupper limit of an adequate content capable of maintaining properties asadhesive is 15 parts by weight. The minimum content showing effects ofaddition of thixotropic agent is 1 part by weight.

[0023] An adequate content of Carmine 6B (Dainippon Ink) as pigment is0.1 to 5 parts by weight.

[0024] As for the epoxy resin, in the case of Epicoat 807 with thecontent of mononuclear components of less than 86% by weight,possibility of damage of components is high. It is Epicoat 806L of 86 to100% by weight that realizes storage stability and other properties andsecurely presents high effects of prevention of damage of components.

[0025] As for the hardener, when Amicure DN23 of amine curing agent isadded, the storage stability drops. When the content of Fujicure FXE1000as latent curing agent is less than 20 parts by weight in 100 parts byweight of epoxy resin, components are damaged, and when exceeding 100parts by weight, the storage stability declines. An adequate content ofthe latent curing agent that can realize storage stability and otherproperties and securely present effects of prevention of damage ofcomponents is 20 to 80 parts by weight.

[0026] Results of review of manufacturing method are summarized below.

[0027] When the epoxy resin and latent curing agent are notpreliminarily heated, the heating sag rate is impaired, and therefore itis preferred to perform preliminary heating in order to maintain theheating sag rate in heating and curing within a practical range.

[0028] When the preliminary heating temperature of the epoxy resin andlatent curing agent exceeds 50° C., the storage stability declines. Inorder to obtain a sufficient storage stability while maintainingpractical properties including heating sag rate, the preliminary heatingtemperature is preferred to be 30 to 50° C.

[0029] Results of review of mounting method of electronic components aresummarized below.

[0030] If the heating and curing peak temperature of the adhesiveexceeds 100° C., components poor in heat resistance may be damaged. Toprevent securely damage of components poor in heat resistance in heatingand curing of the adhesive, the heating and curing peak temperature mustbe kept under 100° C.

[0031] Embodiments and comparative examples are explained below. Table 1shows representative embodiment and comparative examples of components.Table 2 shows representative embodiments and comparative examples in themanufacturing process of the adhesive in the composition shown inembodiment 1. Table 3 shows representative embodiment and comparativeexample of the method of mounting electronic components. TABLE 1Compara- Compara- Compara- Compara- Compara Embodi- tive tive tive tivetive ment 1 example 1 example 2 example 3 example 4 example 5 Epoxyresin A 100 100 100 100 — — Epoxy resin B — — — — 100 100 Hardener A 4015 100 — 40 — Hardener B — — — 40 — 40 Inorganic 5 5 5 5 5 5 fillerThixotropic 10 10 10 10 10 10 agent Pigment 0.5 0.5 0.5 0.5 0.5 0.5

[0032] TABLE 2 Embodiment Embodiment Comparative Comparative 2 3 example6 example 7 Preheating 40 45 25 60 temperature [° C.] Preheating time 240.4  0 10 [hr]

[0033] TABLE 3 Embodiment Comparative 4 example 8 Heating and curingpeak temperature [° C.] 98 110 Heating and curing peak time [sec] 60  60

[0034] Table 4 shows measured results of component damage rate andstorage stability in the adhesives in the composition shown in Table 1.Table 5 shows measured results of heating sag rate and storage stabilityin the manufacturing process of the adhesives shown in Table 2. Table 6shows measured results of damage rate of components poor in heatresistance in the condition of heating and curing peak temperature andtime shown in Table 3. TABLE 4 Compara- Compara- Compara- Compara-Compara Embodi- tive tive tive tive tive ment 1 example 1 example 2example 3 example 4 example 5 Heating sag 0 90 0 0 72 67 rate [%]Storage ◯ ◯ X X X X stability

[0035] TABLE 5 Embodiment Embodiment Comparative Comparative 2 3 example6 example 7 Preheating 1.0 8.2 34.7 0.3 temperature [%] Storage ◯ ◯ X Xstability

[0036] TABLE 6 Comparative Embodiment 4 example 8 Damage rate ofcomponents poor in 0 24 heat resistance [%]

[0037] These results coincide with the overall review results aboverelating to the content of mononuclear components of epoxy resin,component of hardener, inorganic filler, thixotropic agent, pigment,preliminary heating temperature and preliminary heating time of epoxyresin and latent curing agent, and peak temperature in heating andcuring of adhesive.

INDUSTRIAL APPLICABILITY

[0038] The adhesive of the invention, as clear from the descriptionherein, comprises 100 parts by weight of an epoxy resin having a contentof mononuclear components of 87 to 100% by weight, and 20 to 80 parts byweight of a latent curing agent. In this constitution, by thecombination of the epoxy resin having a high content of mononuclearcomponents and the latent curing agent, a large content of hardener canbe blended, and the heating temperature in heating and curing can belowered, so that the adhesive lowered in the damage rate of componentsand excellent in storage stability can be obtained.

[0039] It further comprises 2 to 40 parts by weight of an inorganicfiller, 1 to 15 parts by weight of a thixotropic agent, and 0.1 to 5parts by weight of a pigment, and therefore the adhesive strength isenhanced and stringing is prevented, so that the adhesive havingproperties required as the adhesive for mounting components may beobtained.

[0040] By preparing the adhesive by preliminarily dispersing, heating,dissolving and cooling the epoxy resin and latent curing agent, and thendispersing the inorganic filler, thixotropic agent and pigment, andfurther by defining the heating temperature in heating and dissolving at30 to 50° C. and heating time at 1 to 50 hours, sagging due to heatingcan be prevented, and also time-course changes of the adhesive duringstorage can be prevented.

[0041] In the method of mounting components according to the invention,the adhesive comprising 100 parts by weight of the epoxy resin, 20 to 80parts by weight of the latent curing agent, 2 to 40 parts by weight ofthe inorganic filler, 1 to 15 parts by weight of the thixotropic agent,and 0.1 to 5 parts by weight of the pigment is prepared, and by applyingthe adhesive on specified positions on the board, putting components onthe applied adhesive positions, and heating and curing the adhesive, andit is intended to mount the components without raising the heating andcuring temperature.

[0042] Moreover, when the heating and curing peak temperature in heatingand curing is controlled at 100° C. or less and the heating time within30 to 300 seconds, damage of components poor in heat resistance can beprevented.

[0043] Besides, after heating and curing the adhesive, by applying fluxon the board, the board is immersed in a molten solder, so that thecomponents and board can be soldered and bonded.

1. An adhesive comprising 100 parts by weight of an epoxy resin having acontent of mononuclear components of 87 to 100% by weight, and 20 to 80parts by weight of a latent curing agent.
 2. An adhesive comprising 100parts by weight of an epoxy resin having a content of mononuclearcomponents of 87 to 100% by weight, 20 to 80 parts by weight of a latentcuring agent, 2 to 40 parts by weight of an inorganic filler, 1 to 15parts by weight of a thixotropic agent, and 0.1 to 5 parts by weight ofa pigment.
 3. A manufacturing method of an adhesive composed of an epoxyresin, a latent curing agent, an inorganic filler, a thixotropic agent,and a pigment, comprising the steps of preliminarily dispersing,heating, dissolving and cooling the epoxy resin and latent curing agent,and then dispersing the inorganic filler, thixotropic agent and pigment.4. A manufacturing method of an adhesive of claim 3, wherein the heatingtemperature in heating and dissolving is 30 to 50° C. and the heatingtime is 1 to 50 hours,
 5. A manufacturing method of an adhesive of claim3 or 4, wherein said adhesive comprises 100 parts by weight of the epoxyresin, 20 to 80 parts by weight of the latent curing agent, 2 to 40parts by weight of the inorganic filler, 1 to 15 parts by weight of thethixotropic agent, and 0.1 to 5 parts by weight of the pigment.
 6. Amounting method of components comprising the steps of preparing anadhesive composed of 100 parts by weight of an epoxy resin, 20 to 80parts by weight of a latent curing agent, 2 to 40 parts by weight of aninorganic filler, 1 to 15 parts by weight of a thixotropic agent, and0.1 to 5 parts by weight of a pigment, applying the adhesive onspecified positions on a board, putting components on the appliedadhesive positions, and heating and curing the adhesive.
 7. A mountingmethod of components of claim 6, wherein the heating and curing peaktemperature of the adhesive is 100° C. or less, and the heating time is30 to 300 seconds.
 8. A mounting method of components of claim 6 or 7,further comprising the steps of, after heating and curing the adhesive,applying flux on the board, immersing the board in a molten solder, andsoldering and bonding the components and the board.